[REVIEW] Add memory_usage & items implementation for Struct column & dtype

[galipremsagar]

Description

Fixes: #11893

• This PR implements StructColumn.memory_usage and StructDtype.items

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[wence-]

Can we add a test for memory usage before after nullable?

[codecov]

Codecov Report

Base: 88.09% // Head: 86.88% // Decreases project coverage by -1.21% ⚠️

Coverage data is based on head (c935da5) compared to base (f0b4c4f).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head c935da5 differs from pull request most recent head 668c842. Consider uploading reports for the commit 668c842 to get more accurate results

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #12033      +/-   ##
================================================
- Coverage         88.09%   86.88%   -1.22%     
================================================
  Files               133      133              
  Lines             21982    21995      +13     
================================================
- Hits              19366    19111     -255     
- Misses             2616     2884     +268     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/struct.py	96.47% <100.00%> (+0.41%)	⬆️
python/cudf/cudf/core/dtypes.py	96.67% <100.00%> (+0.03%)	⬆️
python/cudf/cudf/core/udf/strings_lowering.py	0.00% <0.00%> (-100.00%)	⬇️
python/cudf/cudf/core/udf/strings_typing.py	0.00% <0.00%> (-95.78%)	⬇️
python/strings_udf/strings_udf/lowering.py	0.00% <0.00%> (-84.40%)	⬇️
python/cudf/cudf/core/udf/__init__.py	50.00% <0.00%> (-47.06%)	⬇️
python/strings_udf/strings_udf/_typing.py	81.05% <0.00%> (-13.69%)	⬇️
python/cudf/cudf/core/udf/utils.py	97.00% <0.00%> (-2.00%)	⬇️
python/strings_udf/strings_udf/__init__.py	84.31% <0.00%> (ø)

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[wence-]

Thanks!

[galipremsagar]

@gpucibot merge